But CBS's lesser-known new guy, James Corden, besides debuting with strong ratings last week, is off to a hot start online. Though Mr. Corden only started hosting the new show last week, his YouTube channel has exhibited an impressive surge in traffic over the last month.

For example, Mr. Corden's channel’s monthly views jumped from 198,480 on Mar. 1 to 21,878,820 on Mar. 31, according to the Web video analytics firm OpenSlate. Meanwhile, the channel's subscription number has climbed from 26,000 or so a month ago to north of 136,000 as of Thursday.

Mr. Corden is showing some potential. His SlateScore, which OpenSlate calculates using YouTube-compiled date on a channel's viewership, user comments, shares and signs of fan engagement, has climbed from 553 in late February to 608 today. Mr. Fallon and Mr. Kimmel regularly score in the 800-plus range.